Method and system for sharpening teeth on saw chains

ABSTRACT

For users of chain saws it is known that the chain saw teeth should rather often be sharpened by filing in order to keep them well cutting. Traditionally, such a sharpening is effected by means of a straight filing rod moved in a reciprocal manner, but according to the invention it is realized that it is better to arrange the rod as a rotary circular or screw shaped formation, whereby the teeth can be worked in a simplified manner.

The present invention relates to a device for sharpening the teeth ofmotor chain saws. Users of motor saws are familiar with the necessity ofsharpening the teeth on the chain at relatively frequent intervals tomaintain satisfactory cutting, and are well aware that this procedure isdifficult and time-consuming, or is a source of irritation. By itsnature, the problem is particularly familiar to forestry workers.

According to normal standard, the chain saw teeth are filed purelymanually by filing with a round file at a filing angle of approximately30°.

Many devices have been developed to facilitate the sharpening operation,including control of the file alignment. In general, however, theseknown devices for controlling the forward and backward movement of thefile, or even developing a rotary movement of the file, have notachieved widespread practical use.

Also, the use of motor grinding discs has been proposed, with anassocitated fixture for holding the respective teeth of the chain. Apartfrom being troublesome, this method is even dangerous for the teeththemselves, because with a fast running grinding disc this easilyresults in the teeth being excessively heated, whereby their quality canbe drastically reduced.

Chain teeth are in several respects very different from ordinary sawteeth, primarily in having not only an outwardly projecting flankportion, but also an outermost, bent-out top portion, which is to besharpened from below such that the leading edges of both the flank andthe top portion are kept sharp. Therefore, the tooth should be affectedby a filing or grinding pressure in a direction away from the root ofthe tooth, in addition to the force against the flank itself. Thisinfluence is liable to cause the treated tooth carrying chain link totilt outwardly from its position rested against the sword edge, andwhile this can be ‘felt’ and accepted by a manual filing it willnevertheless incur problems in connection with automatic sharpening,inasfar as some backing of the treated tooth is required.

Moreover, the tooth carrying chain links also have, at the end oppositeto and operatively in front of the respective teeth, an outwardlyprotruding “rider”, which is somewhat less protruding than the tooth andhas the purpose of delimiting the intrusion of the tooth into thematerial being sawn and remove the resulting chips. These riders,arranged rather closely in front of the teeth, will to some degreeprevent a grinding disc from entering the teeth in a fully ideal manner,which would be by way of a large disc rotating in a plane parallel withthe chain carrying link in front of the tooth; in practice, however, itcould be sufficient to operate with an inclined position of the plane ofrotation, such that the disc edge will enter into the tooth with thedisc just passing over the top of the rider.

Finally, the teeth of the saw chains appear with a much longer mutualdistance than ordinary saw teeth. Normally there is a number of neutralchain links interposed between the consecutive tooth links, and sincethe consecutive teeth are layed out (or rather in) to opposite sides,the distance between two similarly oriented teeth will becorrespondingly large. Although the chains are made with very highprecision, unavoidable tolerances will cause small deviations of thedistances referred to. The relevance of this observation will appearfrom the following.

Now, in connection with the present invention, it has been recognizedthat a more ideal shape of a rotary grinding or filing tool will be afile rod as first referred to, held against the tooth in exactly thesame position as by conventional tooth filing, now only rounded up so asto form a relatively large circular element rising upwardly from thetooth and turned into an angular position relative to the saw swordcorresponding to the desired filing angle, i.e. an angle of themagnitude 30° from the direction perpendicularly to the sword. In thismanner the filing ring element, in-the local area immediately in frontof the tooth, will appear practically exactly as a conventional filerod, except for a slight curvature thereof, i.e. the ring element willin no way interfere with the said rider in front of the tooth.

According to an important aspect of the invention it will then also bepossible to arrange for means to excert a holding pressure against thetop of the rider belonging to the tooth being filed, whereby the toothor the entire tooth link can be stabilized against the said tilting inresponse to the filing/grinding pressure being applied to the tooth,thus without any need of arranging for a support of the tooth at theopposite side thereof. According to the invention, such means forholding down the riders may be provided even on the ring element itself,viz. as a laterally projecting flange which, during the rotation of thering element, will steadily and slidingly engage the top of the relevantrider and thus stabilize the tooth.

Already by these measures the invention, in practice, provides for asharpening system that will be superior to previous proposals. However,the invention comprises a further and extremely important development,viz. based on the finding that the said circular filing/grindingelement, without any significant change in the character of the localengagement with the single tooth, can be changed from a circular shapeinto three-dimensional screw shape, in which it is able to cooperate,simultaneously, with a number of consecutive teeth. As mentioned, thedistance between the chain saw teeth is relatively long and the filingangle is relatively large, and it has been found that these twoconditions enable the design of a “screw file” having at each place apitch angle corresponding to the desired filing angle and having a phaselength equal to the distance between the teeth, without the diameter ofthis screw being extremely large or small compared with the chain orsword dimensions, this almost amounting to a “lucky coincidence”. Thescrew file, in being rotated about an axis parallel with the movingdirection of the teeth, will thus both sharpen the teeth and urge theteeth forwardly, that is rearwardly relative to their operationalmovement, in order to sharpen the teeth.

The required counter pressure on the teeth for the filing/grinding toolto-effect the desired result may be established already by the inherentresistance against the saw chain being moved along the sword.

Hereby an entirely novel perspective is encountered, viz. that the teethof the saw chain can be sharpened by a continous movement, merely by arotation of the filing/grinding screw element, when the latter ismounted in holding connection with the sword of the chain saw, with itsaxis of rotation held in parallel with the line of movement of thechain. The screw element may be driven at moderate speed, pressingitself against the front side of the teeth and thus forcing the chainrearwardly.

It is a further advantage that the direction of the filing/grindingmovement is the preferred one, viz. with and not against the resultingsharp edges.

The sharpening screw element, just like the said circular filing orgrinding element, may well be provided with the discussed flange memberserving to hold down the riders, i.e. the tooth or teeth may be pushedrearwardly without any noticeable tilting, whereby a high qualitysharpening is achievable by the fully automatic and continuousoperation.

A novelty search based on the invention has revealed that it has earlierbeen proposed to sharpen ordinary saw teeth by means of rotating, screwshaped filing elements, see U.S. Pat. No. 570,732, published in 1896.However, the teaching of this document is impertinent to the sharpeningof chain saw teeth, already because of the above-mentioned fundamentaldifferences between ordinary saws and chain saws. By way of example, inconnection with ordinary saw teeth it would not be possible to operatewith a filing angle as large as 30° with this technique, because betweenthe teeth there would not be space enough for the required tool.Besides, the said document does not indicate the possibility ofmodifying the screw member into a pronounced high pitch member usablefor chain saws.

Moreover, the said U.S. Pat. No. 570,732 does not take into account thediscussed condition with respect to slight variations of the distancebetween the chain saw teeth. The disclosed apparatus is provided withtwo counter rotating screw files for engaging, at the same time, two sawteeth as laid out to opposite sides in the usual manner, whereby the twoscrew members will assist each other in pushing the saw blade (band-saw)in its reverse direction, filing or grinding the two teethsimultaneously. For achieving this result the distance between the twoteeth or any pair of two such teeth has to be exactly the same as theoperative distance between the two filing or grinding screws, as in caseof a slightly larger distance one tooth will be heavily worked while thepressure on the other tooth is relieved and this tooth not workedeffectively, while in case of a slightly shorter distance at least oneof the teeth and/or one of the filing screws may be mechanicallydamaged.

On this background and in accordance with the present invention, thediscussed system should be laid out so as to work only one tooth at atime and as to ensure that the screw element is ready behind the next(or rather second next) tooth when it gets out of engagement with thejust worked tooth. Thereafter and preferably only after the working ofall of the teeth laid out to the same side, the screw tool for workingthe remaining teeth is made operative and the first screw tool is madeinoperative. In practice, the tools are simply interchanged.

Thus, in connection with the invention the problem is not the distancevariations between the teeth of opposite layout, but those between theconsecutive teeth of the same type.

In the following the invention will be described in more detail withreference to the drawing, in which:

FIG. 1 is a perspective view of a row of chain saw teeth and differenttools for filing or grinding the teeth;

FIG. 2 is a lateral view of a saw chain and different sharpening tools;

FIG. 3 is a perspective view of a saw chain and a tool according to theinvention;

FIG. 4 is a perspective view at a preferred tool set according to theinvention;

FIG. 5 is a lateral view of a chain saw sword with the tool set of FIG.4 mounted thereon;

FIG. 6 is a top view illustrating the more detailed layout of the activepart of the tool set;

FIG. 7 is a side view of a filing system for operational and concurrentfiling of saw teeth laid out to opposite sides;

FIG. 8 is a perspective view of a conventional chain tooth; and

FIGS. 9-10 are similar views of teeth shaped according to the invention.

In FIG. 1 is schematically indicated a saw chain 2, appearing with anupstanding saw tooth 4 to be sharpened by filing. Conventionally, thiswould be effected by working the tooth with a straight round file 6 heldat a specific angle relative to the transverse direction of the chaine.g. at an angle of some 30° therewith, by reciprocation of the file 6,though preferably with filing pressure only in strokes with and notagainst the cutting edge. Each tooth has a bent-out top portion 3, theleading end of which is also sharpened by the filing. Every secondtooth, designated 5, is laid out to the opposite side and should befiled by a file 6′ under the same filing angle, but with mirroredorientation relative to the file 6, as shown.

According to the invention it has been found that it is perfectlypossible to imitate the conventional filing by means of a file rod 8rounded up into a circular shape and moved by a rotary motion, passingthe tooth tangentially, whereby its engagement with the tooth will bepractically identical with the effect of the straight file rod 6, thoughnow with the improvement that the ring can be moved unidirectionally inthe correct filing direction as indicated by an arrow A.

This is a basic concept of the invention, enabling a convenient, motordriven operation of the ring member 8.

The saw chain 2 is shown in more detail in FIG. 2. The teeth 4 and 5 arearranged on link members 10, which are interconnected by three otherlink members 12, 14 and 16, and in front of the cutting teeth (i.e. tothe left) the links 10 are shaped with an upstanding “rider” 18determining the intrusion depth of the tooth 4, 5 into the materialbeing sawed. The file rods 6 or 8 will not in any way interfere withthese riders, but in forcing such rods against the teeth 4.5, this willresult in a tilting impact on the entire link 10 about its pivot pin 20underneath the tooth portion 4.5, whereby the tooth may tilt and thuschange the ideal filing conditions.

However, as shown to the right in FIG. 2 and in accordance with thepresent invention, it is possible to combine or provide the filing ringrod 8 with a projecting flange member 22 which, in operation, will serveto prevent any substantial raising of the rider 18, thus also preventingany substantial tilting of the link 10 and therewith the associatedtooth 4 or 5.

According to a further development of the invention it was found thatthe rather distance between two consecutive teeth 4 or 5 laid out to thesame side could be able to condition that the file ring member 8 couldbe converted into a screw member 24 which—as shown in FIG. 3—couldextend along the saw chain, with a pitch satisfying the requirements asto the filing angle and also with a winding length corresponding to thedistance between two consecutive teeth 4 or 5, without the diameter ofthis screw member being excessively “small” or “large”. The saw chainswere never designed with a view to this criterion, and it is to beregarded as a lucky coincidence that the chain teeth will besharpenable/filable/grindable based on the findings of the presentinvention.

In FIG. 3 it is shown that the ring member 8 of FIGS. 1 and 2,originally arranged in an oblique plane of rotation corresponding to thedesired filing angle, is now converted into a screw rod structure 24axis-parallel with the saw chain 2 and having a pitch corresponding tothe desired filing angle of the teeth as well as a winding lengthcorresponding to the distance between two consecutive, similarlyoriented teeth 4 or 5, without the required diameter of the screw rod 24hereby being excessivlely small or large. The screw rod member 24 isshown connected to a central rotary a shaft 26 by means of radial pins28. When the shaft is rotated in the direction R, the screw 24 isrotated so as to effect a movement of the chain 2 in the markeddirection P, and at the same time the teeth 4 are filed as desired.

FIG. 3 merely illustrates the very principle of filing the teeth bymeans of a screw rod. In practice, of course, a more rigid structurewill be required, and besides, as mentioned above, the screw should notbe laid out to work more that a single tooth at a time.

A practical embodiment of a sharpening apparatus according to theinvention is shown in FIGS. 4 and 5. The apparatus comprises a fixturemember 30 having opposed plate portions 32 which, by means of clampscrews 34, can be secured to the sword 36 of a chain saw, with anintermediate bushing portion 38 rising above the top edge thereof. Theportion 38 has a throughhole 40 for receiving a driving shaft 42 of acylindrical body 44 provided with a screw formation 46 comprising aplate strip 48 and a further raised, undercut rod member 50.

In its mounted position as shown in FIG. 5, the cylinder 44 is rotatablee.g. by the chuck 52 of a drilling or screwing machine. It will bereadily understood that by such a rotation the filing or grinding rodmember 50 will be operable to sharpen the teeth 4 successively pushingthe chain rearwardly of its working direction.

Chain saw teeth, unlike ordinary saw teeth, are characteristic in beingslightly movable relatively to each other and to the their commoncarrier structure, inasfar as they are displaceable in all three maindirections. For a high quality sharpening, therefore, it is required tostabilize the teeth—or the tooth being worked, and of course also tomount the fixture member 30 very accurately on the sword 36. In thefollowing, the-conditions in each of the main directions will bediscussed separately:

1. Vertical Direction

The fixture member 30 (FIG. 5) should be mounted such that the lowerside of the cylinder is located parallel with and slightly above thepath of travel of the top of the teeth 4.5 in order to allow the rodmember 50 to properly sharpen the top portions 3. In a preferredarrangement, the cylinder 44 can be replaced by a calibration body orcylinder 54 having a bottom surface which, in the mounted position, islocated slightly closer to the teeth than the bottom side of thecylinder 44, and this calibration body, therefore, can be used foradjusting the fixture body to a correct position, simply by placing thecalibration body on the top of the teeth and tightening the clamp screws34. When thereafter the calibration body is removed and replaced by thecylinder 44, the bottom of the latter will be correctly positioned. Nowthe screw 46 can be rotated or the chain 2 moved to establish filingcontact with a file 4, and from then on the top of the relevant riders18 will be held down by the screwed plate strip 48, at also discussed inconnection with items 18 and 22 of FIG. 2. The leading end of the toothlink 10 will be stabilized vertically by the filing engagement itself.

2. Lateral Direction.

The tooth links are able to move and tilt somewhat in the crossdirection, and for a correct sharpening they should be stabilized inthat direction. To this end, the fixture member 30 comprises a pair ofsliding rail members 56, FIG. 4, preferably made of plastics, which areinsertable along the upper part of the inner sides of the plate portions32 so as to more or less closely fill out the gaps between these sidesand the row of outer rivet heads 58 of the chain links. Thereby theteeth can be sufficiently stabilized, and at the same time the rivetheads will be protected against wear by their sliding along the lowfriction members 56.

3. Length Direction.

As shown in FIG. 6, the screw member 50 should preferably be a littlelonger that the nominal distance between the relevant teeth, such thatthe next tooth can be safely gripped even if the tooth distance, due totolerances, is somewhat longer than the nominal distance. Ideally,therefore in order to allow for both positive and negative tolerances,the leading end E1 of the screw 50 should be able to enter the new toothlink midway between the tooth and the rider thereof, when the workedtooth is just about to be left by the trailing screw end E₂. Thiscorresponds to the screw having an operative length L as shown in FIG.5. The outer end portion E₂ of the screw 50 is made with a pitchsomewhat smaller than the general screw pitch, whereby the driven chainwill slow down a little at the end of the engagement, sufficiently toenable the leading end portion E₁ to catch up with the next tooth(V_(i)>V_(u)) before the first tooth is released from E₂. The endportion E₁ may have the same or even a greater pitch than the generalscrew pitch, whereby it is achievable that the next tooth is engaged soas to take over the driving of the chain at a speed higher that V_(u)thus causing the first tooth to be moved forwardly out of engagementwith E₂, i.e. with a “soft” release of this tooth even if the toothdistance deviates from the nominal distance. In this manner theapparatus will be self-adjusting with respect to the said variations inthe longitudinal direction.

When all the teeth of a first type have seen sharpened, e.g. after 5-10revolutions of the saw chain, the cylinder 44 is removed, and acorresponding, mirrored cylinder is mounted for treating all the teethof the second type, now driven in the opposite direction of the cylinder44. A complete resharpening procedure, typically, will be accomplishedin-some 2-4 minutes.

It should be mentioned that the longitudinal dimension of the chainteeth will-be reduced as the teeth are sharpened over and over, wherebythe free distance between a tooth and its preceding rider (18, FIG. 2)will increase. Therefore, in order to ensure a correct function of theholding plate portion (22, FIG. 2 and 48, FIG. 4) this portion should bebroad enough to effectively cover the rider of both a new and anadvanced ‘filed back’ tooth.

In operation there will be a certain wear on the top of the teeth, sothey will be gradually slightly lower, also because their top side isnormally slanting rearwardly and downwardly such that they get lower asa result of the filing back operations. This will imply a reduction ofthe thickness of the chips, and it is well known that in order to avoidthis effect it can be desirable to file down the riders slightly fromtime to time. In connection with the invention, however, it will beappreciated that it is possible to arrange the plate formations 22, 48so as to be moderately filing or grinding, whereby they will be able togradually reduce the height of the riders.

The filing or grinding rod 8,50 may be adapted to have a higher or lowerefficiency, all according to a desired performance with respect toworking pressure and speed, heat development etc.

The cross section of the filing or grinding rod should not necessarilybe “round”, if only the side portion cooperating with the teeth has therelevant profilation. The riders may be held down directly by thesurface of the cylinder 44, in which case it will be relevant to arrangefor a screw shaped groove in the cylinder for taking up furtherprojecting tooth portions.

In FIG. 7 it is indicated that a very short filing screw portion 60 isarranged for a brief filing of passing teeth 4, while another,complementary filing screw member 62 is arranged for concurrently filingthe teeth 5. As shown the screw segment 60 can be driven with onedirection of rotation by means of a motor shaft 64 of a motor 66, whilethe screw segment 62 can be driven by an oppositely rotating coaxialshaft 68 from the same motor 34.

It is a special aspect of the invention that the short screw section 60and 62 may be provided as integrated parts of a chain saw, i.e. housedinside the outer casing thereof and not being parts of an exteriorfiling apparatus for intermittent use. In this way the teeth can besufficiently and currently filed during their normal operation, or atleast without the mounting of external equipment.

In the latter case the rotation of the shafts 64, 68 should besynchronized with the motor driven chain such that only a slight workingpressure will act on the teeth. The direction of movement of the rods isnot the most attractive, because it will be against and not with thecutting edges, but if the screw segments are operating continuouslyduring the sawing they will not need to be particularly effective, andthis may make the arrangement acceptable anyway.

It should be noted that the screw file may be arranged at the inside ofa surrounding cylinder arranged to be rotated from its outside. Thechain may then be worked in being moved through the screw file.

In the present connection it will apply similarly that an ideal originalshape of the teeth will be as though they have already been filed bymeans of an arched file according to the principles of the invention.This will be of practically no significance for the relatively narrowfiling surface of the vertical flank 7 of the teeth, see FIG. 8, whilefor the horizontal top face 9 with its straight cutting edge 11 a filingoperation with an arched file 12 will start working the opposed endareas marked E, while the middle area M will remain unaffected by thefirst filing operations. Therefore, in order to make the teeth fullysharpenable right from the beginning, the geometry of the top portionsshould preferably be suitably adapted, either as shown in FIG. 9, wherethe cutting edge 11′ is slightly forwardly convex, or as shown in FIG.10, where the top side is slightly grooved in the longitudinaldirection; the latter possibility may be advantageous even for the saweffect of the sharp corner of the cutting edge. The invention willcomprise such chains which are designed particularly for cooperationwith the filing system of the invention.

What is claimed is:
 1. A method of sharpening the teeth of a saw chaincomprising the steps of: moving a file or grinding rod, which is roundedin a lengthwise direction, axially across the individual teeth at adesired sharpening-angle with the saw chain remaining mounted on anassociated saw sword and sharpening a leading edge of both a tooth flankprojecting from the saw chain and a bent-out top portion of the tooth bypositioning and displacing the rod in said lengthwise direction so as tocreate a laterally oriented sharpening pressure against the tooth.
 2. Anapparatus for sharpening the teeth of a saw chain comprising: alengthwise rounded filing or grinding rod which is movable axiallyacross the individual teeth at a desired sharpeng angle with the sawchain remaining mounted on an associated saw sword, wherein the rodsharpens a leading edge of both a tooth flank projecting from the sawchain and a bent-out top portion of the tooth, wherein the rod isunidirectionally positionable and rotatable so as to create a laterallyoriented sharpening pressure against the tooth and a bent-out topportion thereof.
 3. The apparatus according to claim 2, in which thelengthwise rounded rod is a closed ring member, which is operable toengage a chain tooth with the desired sharpening angle in that a planeof rotation of the ring member is turned out of a cross plane of thetooth.
 4. The apparatus according to claim 2, in which the lengthwiserounded rod is spirally coiled, having an axis of rotation extending inparallel with a moving path of the teeth along a selected fraction of achain passage along the saw sword.
 5. The apparatus according to claim4, comprising means for effectively clamping of the saw tooth carryingchain links against local movements during the sharpening of the tooth.6. The apparatus according to claim 5, in which said clamping meanscomprises plate portions associated with the rounded rod positionedthereon such that during the operative engagement between a chain toothand the moving rod, the plate portion will slidingly engage the top of arider located on the same chain link as the tooth.
 7. The apparatusaccording to claim 6, in which the plate portion is of a moderatelygrinding nature.
 8. The apparatus according to claim 4, in which alength of the screw member is slightly longer than a nominal distancebetween consecutive teeth to be sharpened, and in which a pitch of thescrew member is smaller at an end of tooth delivery than at a leadingend of the screw member.
 9. The apparatus according to claim 4, in whichthe screw member is arranged on a cylinder, which is rotatably mountablein a fixture member to be fastened to the saw sword, the cylinder beingexchangeable with another, mirrored cylinder for sharpening, withopposite direction of rotation, those teeth which are laid out to theopposite side.
 10. The apparatus according to claim 4, wherein theapparatus is integrated in a housing of a chain saw.
 11. The apparatusaccording to calim 3, comprising means for effectively clamping of thesaw tooth carrying chain links against local movements during thesharpening of the tooth.